The present disclosure generally relates to radial bearing systems and more particularly, to shock absorbers for radial bearing systems in downhole drilling assemblies.
In the drilling of wells for exploration and/or production of hydrocarbons, downhole drilling assemblies are often operably disposed near a drill bit in a sub-surface formation to rotate a drill bit rather than rotating an entire drill string. In such drilling operations, the drill string includes joined lengths of pipe that extend down into a wellbore.
These types of drilling assemblies usually contain a fluid-driven motor that is typically attached to the bottom end of the drill string. For example, a “Moineau” or progressive-cavity type motor may be operated by the flow of drilling fluids pumped down through the drill string from the surface. The motor drives an output shaft which is in turn coupled to a drill bit to rotate the drill bit.
Drilling fluid or mud is pumped down the drill string to the drilling assembly to drive the fluid motor. The mud is pumped into a casing at a predetermined pressure. The pressurized mud rotates the output shaft and correspondingly, the drill bit. The drilling mud leaving the motor is directed through the shaft to the bit and through well bore to cool the bit and remove rock fragments from the well.
Various components of the drill string are subjected to axial vibrations, thrust loads, and shocks during drilling operations. These typically high dynamic stresses and/or vibrations on the drill string may be substantial, particularly during drilling operations in hard and/or non-homogeneous formations. It is desirable to minimize the transmission of such vibrations to reduce the exposure of the components of the drill string to thrust loads. Specifically, it is desirable to dampen axial vibrations and shocks to components such as instrumentation that may be disposed along or within the drill string. Further, dampening axial shock is helpful in reducing bit bounce (i.e., the inability of a drill bit to maintain engagement/contact with the formation) thereby, increasing the rate of penetration of the drill bit and increasing the overall efficiency of the drilling effort.
Conventional approaches to dampen or otherwise absorb axial vibrations and shocks during drilling suffer from a number of disadvantages. Specifically, some conventional shock subs do not function optimally because the shock subs are typically disposed upstream of the bit at a distance that is too far from the drill bit to most effectively dampen axial vibrations.
In addition, conventional shock subs are typically incapable of fully reducing bit bounce. Excessive bit bounce typically results in reduced efficiency and shortens the lifespan of the drill bit. In addition, conventional shock subs may transmit excessive vibration along the drill string, damaging sensitive electronic components and other components of the drill string. Furthermore, conventional shock subs are sensitive to hydraulic flow through the downhole assembly. Specifically, hydraulic flow through the assembly significantly impedes the dampening characteristics of the shock sub. Still further, fluid flow through the shock sub significantly influences the telescopic extension of the shock sub. These effects limit the operating range of the shock sub and restrict the ability of the shock sub to function properly under certain conditions. In summary, these complexities adversely complicate the design and operation of the conventional shock sub.
Another disadvantage of some conventional shock sub designs is the excessive additional length that is introduced in the downhole assembly when a motor is attached to the drill string. This additional length may be particularly undesirable in instances where it is desirable to minimize the distance between the drill bit and the shock sub. As would be understood by those of ordinary skill in the art, it is desirable to locate the shock sub as close to the drill bit as possible to achieve maximum efficiency.
Accordingly, an improved shock sub design is needed to address the above-identified disadvantages of the prior art.